Solar physicist David Hathaway has been checking the sun every day
since 1998, and every day for six years there have been sunspots.
Sunspots are planet-sized "islands" on the surface of the
sun. They are dark, cool, powerfully magnetized, and fleeting: a typical
sunspot lasts only a few days or weeks before it breaks up. As soon
as one disappears, however, another emerges to take its place.

Even
during the lowest ebb of solar activity, you can usually find one
or two spots on the sun. But when Hathaway looked on Jan. 28, 2004,
there were none. The sun was utterly blank.

It happened again last week, twice, on Oct. 11th and 12th. There
were no sunspots.

"This is a sign," says Hathaway, "that the solar minimum
is coming, and it's coming sooner than we expected."

Right:
The blank sun on Oct. 11, 2004, photographed by the ESA/NASA Solar
and Heliospheric Observatory.

Solar minimum and solar maximum--"Solar Min" and "Solar
Max" for short--are two extremes of the sun's 11-year activity
cycle. At maximum, the sun is peppered with spots, solar flares erupt,
and the sun hurls billion-ton clouds of electrified gas toward Earth.
It's a good time for sky watchers who enjoy auroras, but not so good
for astronauts who have to be wary of radiation storms. Power outages,
zapped satellites, malfunctioning GPS receivers--these are just a
few of the things that can happen during Solar Max.

Solar minimum is different. Sunspots are fewer--sometimes days or
weeks go by without a spot. Solar flares subside. It's a safer time
to travel through space, and a less interesting time to watch polar
skies.

Hathaway is an expert forecaster of the solar cycle. He keeps track
of sunspot numbers (the best known indicator of solar activity) and
predicts years in advance when the next peaks and valleys will come.
It's not easy:

"Contrary to popular belief," says Hathaway, "the
solar cycle is not precisely 11 years long." Its length, measured
from minimum to minimum, varies: "The shortest cycles are 9 years,
and the longest ones are about 14 years." What makes a cycle
long or short? Researchers aren't sure. "We won't even know if
the current cycle is long or short--until it's over," he says.

Above:
Astronomers have been counting
sunspots for centuries. This plot shows sunspot numbers from 1610
to 2000. Data are also available for the current cycle (1996-2004):
click
here.

But researchers are making progress. Hathaway and colleague
Bob Wilson, both working at NASA's Marshall Space Flight Center, believe
they've found a simple way to predict the date of the next solar minimum.
"We examined data from the last 8 solar cycles and discovered
that Solar Min follows the first spotless day after Solar Max by 34
months," explains Hathaway.

The most recent solar maximum was in late 2000. The first spotless
day after that was Jan 28, 2004. So, using Hathaway and Wilson's simple
rule, solar minimum should arrive in late 2006. That's about a year
earlier than previously thought.

By that time, according to NASA's new vision
for space exploration, robot ships will be heading for the moon
in advance of human explorers. If Hathaway and Wilson's prediction
is correct, those robots will need good shields. Solar flares and
radiation storms can damage silicon brains and electronic guts almost
as badly as their organic counterparts.

For now, says Hathaway, we're about to experience "the calm
before the storm." And although he's a fan of solar activity--what
solar physicist isn't?--he's looking forward to the lull. "It'll
give us a chance to see if our 'spotless sun' method for predicting
solar minimum really works."